A buckle including a male member and a female member, as described in Patent Document 1 and Patent Document 2, has been conventionally known.
The male member described in Patent Document 1 includes a pair of arms each having an engaged part at its front end, which is symmetric about a plane, and extends from a bottom. The female member includes a flat cylinder-shaped storage part having an insertion port, into which the pair of arms is inserted, to store the pair of arms in the storage part. A through hole that engages with the engaged parts of the male member is formed in an inner surface of the storage part of the female member. In the state where the male member is coupled to the female member, front ends of the arms do not contact a wall surface opposed to the insertion port, and are stored in the storage part.
The female member described in Patent Document 2 includes a flat cylinder-shaped storage part having an insertion port, into which arms are inserted, and engaging parts that engage with the engaged parts of the arms are formed on an outer edge of an opening opposed to the insertion port. In the state where the engaged parts of the male member engaged with the engaging parts of the female member, the front ends of the arms are exposed from the opening opposed to the insertion port.